If the water stays in the hot tub for quite some time in the summer without treatment, it may cause algae and fungi. For more information, please see Water Treatment. You may clean the water with our offered filter system or with some other similar product. The Complete Pond Filter System which we offer takes the guesswork out of complicated pump and filter selection. Compact, submersible pond filtration system provides mechanical and biological filtration. It is also good to use some water care products based on active oxygen, which have benefits over traditional sanitizer methods.